The naturally-occurring phagocytosis-stimulant peptide-tuftisin comprises a fragment of a heavy chain of human immunoglobulins of the class IgG (Thr-Lys-Pro-Arg). This tetrapeptide reveals a stimulant effect relative to numerous immunological reactions both in vivo and in vitro; thus it substantially stimulates the phagocytic activity of leukocytes and macrophages (cf. Cytobios, vol. 6, No. 21-22, 1972; A. Constantopoulos, V. A. Najjar "Tuftisin, a natural and general phagocytosis stimulating peptide affecting macrophages and polymorphonuclear granulocytes", p. 97-100).
It is known from the literature that tuftisin can be useful as a medicated compound for substitution of .gamma.-globulin in the treatment of diseases associated with decreased activity of leukocytes, as well as in spleenectomy and certain disturbances of spleen which are accompanied by considerable reduction of the organism resistance to infectional diseases. (Cf. J. Pediat., vol. 80, No. 4, 1972; A. Constantopoulos, V. A. Najjar, J. W. Smith "Tuftisin deficiency: a new syndrome with defective phagocytosis", pp. 564-567).
Known in the art are numerous synthetic analogs of tuftisin formed by modification of one or two aminoacid moieties of the molecule (Int. J. Peptide Protein Res. Vol. 9, N 1, 1977; D. Konopinska, E. Nawrocka, I. I. Siemion, S. Slopek, St. Szymaniec, E. Klonowska "Partial sequences of histones with tuftisin activity", 71-77, Biochim. Biophys. Acta, Vol. 496, N 1, 1977; M. Fridkin, Y. Stabinsky, V. Zakuth, Z. Spirer "Tuftisin and some analogs. Synthesis and interaction with human polymorphonuclear leykocytes", 203-211).
However, these modified analogs of tuftisin possess but an insufficient phagocytosis-stimulating activity as compared to natural tuftisin.